Electrical musical instrument



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NOTE No e5 June 10, 1941. v 1 HAMMOND 2,245,337

ELECTRICAL MUSICAL INSTRUMENT Filed Sept; 12, 1938 3 Sheets-Sheet 2 189 193 Mera@ I ldaafefajlmmond 0@ M Hyg June 1o, 1941. L HAMMOND 2,245,331

ELECTRICAL MUSICAL INSTRUMENT Filed Sept. l2, 1958 3 Sheets-Sheet 3 Patented June 10, 1941 UNITED STATES PATENT OFFICE ELECTRICAL` MUSICAL INSTRUMENT Laurens Hammond, Chicago, Ill. Application September 12, 1938, Serial No. 229,447 14 claims. (c1. x4-1.26)

My invention relates generally to electrical musical instruments, and more particularly to instruments of this kind which are capable of producing a wide variety of musical tone qualities, similar in musical results obtained, and in the method of playing, toa large well builtand voiced pipe organ.

In accordance with the principles of my invention, various tone qualities are produced by combining partiels derived from sources of different frequencies corresponding to those of the tempered musical scale. The partials may, however, themselves be complex waves, each comprising a fundamental and a plurality of harmonies, or, each of the p'artials may consist of impulses of substantially sine wave form. Thus, the player has at his commands. method of producing music which approximates very closely that employed in the better pipe organs, but which, in many respects, is superior to the'music obtainable from such pipe organs.

It is thus among the objects of my invention to produce an improved electrical musical instrument in which:

(l) Pipe organ like music of a quality superior to that previously obtainable by any known instrument may be obtained; I

(2) The electrical impulses are generated by electrical means having no moving parts;

(3) The tones produced will have gradual attack and decay characteristics;

(4) The quality of the tones may be easily varied throughout an exceedingly wide range;

(5) Vibrato and tremolo effects may be produced at will;

(6) Adjustable resonance output circuits may be employed to attenuate certain selected frequency ranges;

(7) Tone qualities may be rapidly selected and varied;

(8) Relatively high voltages are employed in the key circuits, but the major portions of the circuits operate at low potentials;

(9) Key operated switches close circuits of high voltage and low amperage, making practical the use of simple and economical switches;

(10) The harmonic development of the impulses supplied by the generatorsmay be rapidly varied;

(11) Electron discharge devices operating'far below their current carrying ratings are utilized for generating the electrical tone frequency ims pulses as well as.. for controlling the'transmission of these impulses to the output circuitsof the instrument, and thus will have a life greatly exceeding their life under normal use in other ins trumentaliti es (12) Tones veryrich in harmonic development may be produced;

(13) Key switches close very high impedance circuits which may be connected in parallel without appreciable robbng;

(14) 'Ihe transmission of each simple or complex partial to the output circuit is governed by a single control tube and the operation of each control tube is determined by a plurality of high impedance key switch closed circuits, and;

The instrument may be played using customary organ technique to produce music of the organ type far superior to that obtainable by any previous instrument of this class.

A further object is to provide an improved expression pedal apparatus whereby the intensity of notes played on one of the manuals may be changed at will with respect to notes played on the other manual, or with respect to the notes played on the pedal clavier.

Other objects will appear from the following description, reference being had to the accompanying drawings, in which:

Figures 1a and 1b together constitute a schematic Wiring diagram of representative portions of the instrument.

Figure 2 is a circuit diagram illustrating a l-'modified form of the invention and incorporating tremulant producing apparatus, and an expression apparatusvfor each of the manuals as well as for the pedal clavier.

In general, the instrument will comprise a console having two or more manuals, a complete pedal clavier, a plurality of preset keys or tablets for each of the manuals and for the pedal clavier, with or without a piston controlled capture system whereby a plurality of preselected preset keys may be simultaneously selected by operation of the piston in accordance with conventional pipe organ console practice.

The console will also be provided with a vibrato control mechanism whereby the degree of vibrato effect may be regulated, a tremolo controlling means whereby the degree of tremulant, and, if desired, also the frequency of the tremulant may be controlled. In addition, the instrument will be provided with suitable controls for adjustablev resonant output circuits by y which certain predetermined frequencies may be attenuated.

In addition to the Apreset keys or tablets by which the instrument may be conditioned to produce predetermined4 tone qualities, the instrument will preferablyfbe provided with draw bars ,the highest frequency stage,

orV the like, each individually adjustable, to control the relative intensities of the partials of the 'tone to be produced. Controls will also be proamplifier to' vary its effective gain, or otherwise.

connected in the output circuit to control the amplitude of the impulses transmittedV to the electroacoustic translating means.

Frequency generating system While the frequency generating system employed to supply the electrical impulses of the fundamental frequencies of the tempered musical scale might be of any one of a number of different types, I prefer to employ a system in which electron discharge tube oscillators are used to supply the twelve frequencies of the notes of the highest pitch octave of the instrument, and in which each lof these oscillators serves as a high frequency source for twelve series of cascaded frequency divider stages. In this system each stage is perse non-oscillatory, but is capable of supplying a signal having a fundamental frequency one-half of that of the regulating frequency which is supplied to it by the next higher stage of the cascaded series, and, with respect to the signal supplied by its associated oscillator. A frequency generating system of 'this type is fully `disclosed land claimed in my co-pending application Serial No. 199,614, filed /April 2, g 1938, which has matured into Patent No. 2,126,682, granted August 9, 1938.

In itsusual form, tlie instrument will be pro- |09 and a condenser |I0. The frequency of resonance of the oscillatory circuit including the variable inductance |08 and the condenser I I0 may be periodically varied by a vibrato mechanism, shown as associated with this circuit and which will hereinafter be described in greater detail. 'I'he oscillator for the note 85 provides a signal of a frequency of 4186.01 c. p. s., which is transmitted through a condenser Ca, and a resistor R3 to the control vgrid I I2 of a divider tube DT13 for the note 13.

The divider tube is preferably a pentode with sharp cut-off characteristics, a tube of the type known as 6J7 being satisfactory. The screen and vided with `a plurality of manuals ranging from the musical note C1 to the note Cs, while the pedal clavier will range from Cn to Ga. For convenience herein, the various Anotes will be num'- bered successively, the note Cn beingV designated note I-and note Ce being designated note 13. In addition to providing means for supplying frequencies for the notes I to 13 inclusive, means are provided for supplying frequencies to 96 inclusive, the latter being utilized as partials for notes 38 to 13 inclusive. Thus, although there are no keys corresponding to notes 'I4 to 96 inclusive, the latter notes are utilized as harmonics in synthesizing notes for. which keys are provided,

and, if desired, notes 14 to 96 inclusive may be sounded'separately by proper manipulation of the draw bars, or by adjustment of the preset key circuits.

As previously stated, the electrical impulses for the twelve highest notes, Nos,-05 to 96 inclusive,

are produced by vacuum tube oscillators, the oscillator for note No. 85 being shown in Figure la as representative of these twelve oscillators. This oscillator is illustrated as comprising a pair of for notes 14V the suppressor grid of the tube DT13 are connected to suitable sources of direct current potential, indicated in Figure la as being of +100 v.` and +45 v, respectively.

A resistor R4 is connected between the grid I I2 of tube DT13 and the terminal C of fixed direct current potential illustrated as being of ground potential, the grid being connected to the cathode by a condenser Cb. A condenser Cc connectsthe cathode to a terminal B likewise indicated as of ground potential, while a resistor R6 connects the cathode to a terminal A of fixed direct current potential indicated as being at -100 v. A resistor R5 connects the plate of tube DT13 to a terminal D indicated as being of +300 v.,

while the plate is connected to a terminal E of consta-nt direct current potential, indicated as ground, through a condenser Cd. In Figure 1a, the circuit diagram for the rst stage only ofthe frequency divider system is illustrated in detail, since the remaining stages are identical with theY stage for note 13 except that the values ofthe con` densers and resistors will vary from stage to stage. In the two lowest frequency stages the circuit may, if desired, be slightly modified as disclosed in. my aforesaid Patent No. 2,126,682. The signal from the tube DT13 is derived from voltage fluctuations of its cathode through a condenser Cf which is connected between the cathode and the grid |40 of a control tube CT13.

'The stages for'the notes Nos. 13, 6I, 49, 31, 25, I3 and I are connected in cascade with the grid of the tube DT13 receiving asigna] from the oscil.

cessively halves the frequency supplied to it, and` impresses the halved frequency upon the succeeding stage as a controlling signal, Since the operation ofthe frequency divider system is fully disclosed and claimed in my aforesaid Patent No.

2,126,682, and since per se it does not form a part of the present invention, the operation of the system will not be further described herein. In so far as the present invention is concerned, any other triodes |00 and |02 which are shown las separate v tubes, but in actual' practice wouldcrdinarily be combined in the form of a'twin triode. 'The plate of tube |02 is connected'th'rcugh a condenser |04 and' resistance |06 with the grid of the tube I 00 to provide the yfeedback, while-'the frequency of osu cillation is controlled by a resonant circuit coupled to the grid of tube |00 and comprising a special high efiiciency construction variable inductance 1s preferably of saw tooth shape, which, when suitable sources of the frequencies of the various notes of the musical scale might be utilized in place of the divider system shown, provided that such sources are capable of producing signals of the desired wave form and amplitude. The wave transmitted through the distortion and control tube, provides a signal which may be analyzed into a fundamental and a long series of harmonics of successively decreasing amplitude. While this wave formis preferred, it will be apparent to those skilled in the art that many of the desirable results of the present 4invention may be obtained even though the sources produce waves of the simplest character, such as substantially pure sine waves.

Control tubes plate circuit of the triode |00,'being conducted through a resistance |44 and condenser |42, the grid |40 of this tube being connected to ground through a resistance |50 which, upon operation of a switch, may have a resistor |48 connected in parallel therewith. In the case of the control tubes connected to the stages of the frequency divider system, of which the control tube CT13 is representative, the signal derived from the cathode of the divider tube DI'13 is impressed upon the grid |40 of control tube CT13, and the latter grid is connected to ground through a resistor |52 connected in parallel with a condenser |54. vA mute condenser |56 is adapted to be selectively connected in parallel with the resistance |52 and condenser |54 by a suitable switch. The switches which control the connection of the condensers |56 in parallel with the resistance |52 and condenser |54, as well as the switches which are adapted to connect the resistances |48 in parallel with resistances |50, are preferably provided with an actuator which is common to the corresponding switches for all of the notes of the instrument, or, if desired, a plurality of actuators may be provided, each operating va group of these switches. 'I'he screen grid |58 of the tube CT13 is suitably connected to a source |60 of adjustable direct current potential, while the suppressor grid |62 may be connected to a similar source, indicated in Figure 1a as ground.

The tube CT13 is normally biased sufficiently beyond cutoff so that it will not transmit the signal which is continuously impressed upon its grid. The control tube is preferably a pentode having sharp cutoff characteristics, such as are found in the type 606, which tube has a cutoff voltage of approximately -6 v. Thus, as long as the cathode of the tube CT13 is maintained at a potential of slightly more than +6 v. with respect to ground (since the grid is connected to ground through resistor |52), the tube will remain non-conducting. The amplitude ofthe signal transmitted by the of. .trol tube is determined by the cathode-plate current of this tube, which in turn is controlled by suitable key switch circuits. The cathode-plate current of the control tube may be considered as being chopped off by the signal impressed upon its grid. The control of the cathode-plate current of the control tube CT13 is accomplished by means of the key operated switches as follows:

The cathode of thecontrol tube CT13 is connected to a terminal N, which inturn is connected to ground through a condenser C4. The terminalN is connected to a terminal M through a resisten y the terminal M to ground. The resistance of R1 maybe in the order of 10,000 ohms. Key operated switches are provided to impress selected potentials upon the terminal -M, and because of the resistor; R1, the potential impressed upon the terminal M R1, and thecondense-r C1 connects" times that of will substantially control the lmay conveniently be twelve amplitude of the cathode-plate current through the tube CT13.

In the drawings (Figs. la and 1b) ar illustrated four keys, K-l3, K-31, K-Sl and K13 which are representative of the keys of the manuals of the instrument, and are likewise generally representative of the keys of the pedal clavier. Each of these keys when depressed causes its'associated switch fingers |10-|18 ln-v clusive to be flexed downwardly and make contact with bus bars 08 inclusive respectively. Each of the switch fingers |10-|18 has one terminal of a resistor |80 connected thereto, the resistor being preferably in close proximity to the switch finger, the other terminal of each of the resistors |89 being connected to one of the terminals M. lThe resistors |88 are preferably of -high value, for example, 500,000 ohms. The wiring system for the key switches may be described briefly as follows:

The switch finger |16 is connected to the terminal M of the control tube generating the fundamental frequency corresponding to that of the key. For example, the switch nger |16 for the key K-13 is connected to the terminal M for control tube CT13. The switch finger |15 is connected to the control tube for the note which has a frequency twice that of the note to which the switch finger |16 is connected, and thus con-` trois the supply of a signal having as its fundamental frequency, the second harmonic of the note of its associated key. Similarly, the switch fingers |14, |13, |12, |1| and |10 control the Itransmission of frequencies corresponding respectively to the third, fourth, fifth, sixth and eighth harmonics of the note represented'by the Ikey with which they are associated. The switch nger |18 controls the transmission of the suboctave frequency, while the switch finger |11 controls the transmission of a frequency which is the third harmonic of the sub-octave frequency, namely, a frequency substantially 1.5

the fundamental frequency.

The potentials upon the bus bars |80| 88 inclusive may be selectively controlled by one of two methods. It will be understood that a separate set of bus bars, such as |80-|88, will be provided for each manual and for clavier, and each set ciated therewith a plurality of preset keys which mately ten of the preset keys being operable to connect the bus bars |80|88 inclusive to preselected dlrect current potential sources, while two of the preset keys may be utilized to connect the associated 'bus bars with draw bars by means of which vthe potential on each of the bus bars may be individually controlled.

In Figure 1b there are illustrated -two preset keys PK-I and PK|0 representative of the group of preset keys by which direct current potentials of pre-,selected values may be impressed upon the various bus bars M30-|88. Each of the preset keys such as PK| and PK|0 is adapted, upon depression, to flex switch arms |90|58 inclusive into contact withbus bars |80|88 incluslve. The switch arms |9 0|98 inclusive are adapted to be connected by means of conductors 200 with any one of a plurality of conductors 202-2I0 inclusive. In the instrument the conductors 2022| 0 may be in the form of bars hav--V the pedal of bus bars will have assoin number, approxi 4 to successive taps on a voltage divider 2|2 which is vsupplied with current from a suitable direct current source 2I4, a protective resistance 216 of suitable value being in series with the voltage divider 2I2 and voltage source 2&4 to prevent damage should the voltage divider resistance be accidently short-circuited. An intermediate tap of the direct current source 244 is preferably grounded so that the conductor 202 is normally at a potential above ground, in the particular construction disclosed, being illustrated at a p' tential of +6 v. f

device 240, the latter being resistance-coupled through a preamplier 242 and power amplifler 244 to a loud speaker system 246, the preamplifier and power amplifier being, as customary, supplied with current from a suitable power supply system.

By way of illustration, the taps of the voltage divider 2l2, which 'are connected to the con ductors 202-2I0 inclusive, aremdicated as impressing the following voltages upon said conductors respectively: +6, 20, 50, 75, 111, 175, 250, 350 and 500. With these gradvnations in voltages, the increments in loudness of the notes produced Will'appear to be. substantially equal. The chassis carrying the key switches is preferably connected to the terminal 202 which is at +6 v., so that any current leakage from the key switches will notresult in the sounding of a note.

A plurality of draw bars 2I8 are each provided with a contact making member 220, the `draw bars being longitudinally slideable to any desired position of adjustment to bring their 1respective contactors 220 into contact with contact bars 222-230, which are connected respectively to conductors 202-2I0 inclusive. 'I'he draw bars 2I8 are connected respectively with switch fingers i90-.|98 inclusive which are actuated lby a preset key -PK- TL the connection being made through ilexible conductors 232.l When the preset key is depressed, and held indepressed po\ vsition by a suitable latching means, (as shown in my prior Patent No. -1,956,350) it Will be apparent that the draw bars 2l8 will be connected to the bus bars IBG-|88 inclusive respectively, and that by manipulation of the draw bars, each vof the bus bars may be connected to any selected one of the taps of/the voltage divider. ItI will be f understood that there will be two 0r more preset keys similar yto the preset keyy PK-l I, and an equal number of sets of draw bars 218 for each manual, and that the pedal clavier is likewise provided with a set of draw bars, although in the case of the pedal clavier,'it is not essential that all ofthe partials be individually controllable as to intensity, and the draw bar system for the pedal clavier may therefore be simplified to the extent desired.

Theplate circuits of thev control tubes CTI- CT13 inclusive are connected to a common source of B current supply through a conductor Vibrato producing means The effectiveness of musical tones isgenerally speaking, greatly enhanced for certain'purposes. by causing its frequency to shift over a limited range at a periodicity of 6 or 7 c. p. s. In the instrument of my invention, means for producing such vibrato frequency shift comprises aplurality of condensers 248 which, by means of switches 250, may selectively .be connected in .parallel with a, portion of inductance |08. There is a set of condensers 248 for each of the twelve oscillators and the corresponding switches 250 of each of the oscillators are mechanically interconnected for simultaneous operation.

Two of the condensers 248 are adapted to have one of their plates grounded through a switch 252 .which completes a circuit. through a vibrating reed 254. There may be six reeds 254 (of which only two are illustrated) and each is .vi-,- ,brated at a slightly diierent frequency, being actuated by anv electromagnet 256 which is energized from al suitablesourceof current through an interrupter circuit completed through the reed during a portion of 'the oscillatory cycle of the latter. By having the reeds 254 tuned to slightly different frequencies,l all close to 7 c. p. s., six slightly-different vibrato frequencies will be impressed upon the twelve oscillators. By connecting oscillators for adjacent semi-tones to the same reed, most of the notes of a chord normally sounded during playing customary music will have a diierent'vibrato frequency, since it is rather the exception to have a chord include adjacent semi-tones or notes separated by an 0ctave plus orminus a semi-tone.

The values of the condensers 248 which have' one side thereof permanently connected to ground 233 and a resistance 234. Inthe diagram, the

plates of all of these tubes are indicatedas being connected in parallel. In the actual instrument, the plates will, however, preferably be connected in parallel groups of approximately four hotes each, and the common conductor for each group supplied with an adjustable Aiilter pad whereby each group of four notes may be separately voiced to produce the most desirable musical effect. A system ofv this character is fully disclosed in my Patent No. 2,126,464, dated August 9, 1938.

In the simplified circuit disclosed herein,.the

signals from the control tubes are fed throughv conductor 233 and condenser 238 to adjustable resonant output circuits 236, and the signal is fed from the resonant output circuits to a volume or vexpression control and adjustable tremulant are such, with respect to their associated condensers, that upon changing the positions of the switches250, the average frequency of the associated oscillator will not be altered. By having the condensers 248 connected in parallel with only a portion of the inductance |08, the condensers 248 may be made of greater capacltances So that the distributed capacity of the wires and switches connected to these condensers will be small relative to the -values of the condensers, and thus have but a negligible. eifect.

The vibrato mechanism is morek fully disclosed and claimed in my co-pending applicationv Serial No. 199,612, filed April 2, 1938.

Operation The instrument is operated in the mannerof an organ and is capable of rendering, with a high degreeof satisfaction, the classical works of organ literature.

After depressing the desired preset key, assuming the supply of power has been connected to the oscillators, frequency dividers and amplifiers, the instrument may be played in the usual-manner .by depressing the playing keys KI- K`|3. Upon depression of a key, for example, X31, the potentials of terminals M associated with the control tubes for the frequencies which are partials of the note 31 will each lbe changed ratherf.

gradually to the lpotential of the bus bar I-I68 to which the terminal is connected.

|89 and the resistances R1, the fact that a single terminal M may be connected to a plurality of different lbus Ibars through the different key switch circuits is not appreciably disadvantageous. This may be shown by computing the current flow through the resistor R1 under several different conditions of operation, since it is the current ow through the resistance R1 which determines the amplitude of the output .signal of the control tube.

For example, let us assume that the cutoff voltage ofthe control tube is 6 volts and that the terminal M is connected through only one key switch circuit to a bus bar, the potential of which is -500 volts, making the potential difference which causes current to flow through the resistors |89 and R1, 506 volts. Since the total resistance of this circuit is 510,000 ohms, the current flow (after a steady state has been attained) will be .993 ma.

As a further example, let us assume that the terminal M is connected through two key switch circuits to two bus bars, one having a potential of -500 volts, and the other having a potential of -6 volts. It may readily 4be computed that under these conditions, the current ow through the resistor R1 will amount to .975 ma.

As a further example, let us assume that a terminal M is connected through two key switch circuits to two Ibus bars, each of a potential of -500 volts. Under these circumstances the current ow through the resistor R1 will amount to 1.950 ma.

From the three foregoing examples, it will be seen that the current flow through resistance R1, and hence the amplitude of the signal, is reduced only from .993 ma. to .975 ma. when the terminal M ls not only connected to a 'bus bar of -500 volts, but in addition is connected to a bus bar of -6 volts. The undesired reduction in the amplitude of the signal under these circumstances is thus less thany 1.85%, a reduction in amplitude which would not be perceptible to the normal ear.

Similarly, when the terminal M is connected through vtwo key switch circuits to two bus bars, each of U0 volts, the current. flow through resistor R1 will be 1.950 ma., whereas it should, strictly speaking, be 2 .993 ma., or 1.986 ma. The reduction in amplitude of the signal is thus again less than 1.85%, which is imperceptible to the ear. Of course under extreme conditions, when a terminal M is connected to a large plurality of bus .bars of different potentials, the reduction in amplitude of the signal due to the robbing effect may be greater, but this will occur only when playing a chord having a large number of harmonically related notes. Under these circumstances it is not disadvantagous that so-me robbing takes place. The musician is accustomed to this effect because it takes place whenever a plurality of organ pipes of the same pitch are sounded simultaneously, or whenever a plurality of instruments play the same note, since there is a certain amount of interference between the partials of the several sound producing bodies, so that there is never a true arithmetical addition of the amplitudes of the partials. This effect is of course obvious whenQit is .considered that there is practically no possibility whatsoever that partials of the same `frequency produced .by different sources will be exactly in phase, and there will therefore be some cancellation of the partials from one source by the partials produced .by the other sources.

The tones produced .will have a quality which will be dependent upon the various voltages on the bus bars ISU-|88 as determined by the particular preset key which has been operated. 'I'he tone may be made of relatively simple character by holding the reeds 254 against vibration by any suitable vibrato controlling means and by closing the switches which connect the condensers |56 in parallel with the condensers |54. If it is desired to render the tone more complex, the switches for the condensers |56 may be opened, whereupon the signal from each of the control tubeswill in itself contain a large number of partials so that the musical effect will be that obtained by the sounding of a plurality of organ pipes or the like. Since, speaking generally, the trained musical ear prefers a tone in which the acoustic energy is distributed over a wide range of frequencies, it will be apparent that under these circumstances a beautiful, Vrich and full tone will be produced.

The warmth of the tone may be increased by rendering the vibrato mechanism operative. The vibrato mechanism has the effect of adding further richness to the ltone since it adds new and different frequencies. As previously stated, there are preferably six diierent vibrato rates since the reeds vibrate at slightly diierent frequencies. Thus, when a plurality of notes are being simultaneously sounded they will be shifting in frequency at different rates in a substantially random manner, so that the musical eilect will be an increase in the warmth, fullness and richness of the tone rather than the elect of a definite vibrato or tremolo. There will be so many changes in the frequencies going on simultaneously that the ear is unable to analyze the various changes in tone which are occurring, and the listener thus obtains only the aggregate impression of a beautiful satisfying tone quality. Of course the degree of vibrato effect may be varied in any one of three gradations by optional operation of the switches 250.

When the player desires to produce a tone which is not available on depression of one of the preset keys PK| to PK-IU, he-will utilize the draw bars 2|8 to pre-select the tone quality, rendering the draw bars effective by depression of an associated draw bar control key, such as PK-I With the draw bar control, the musician may select any one of myriads of tone colors, merely by setting the draw bars to the desired one of countless possible combinations.

In order to prevent short circuiiting of the battery 2N, or short circuiting one or more sections of the voltage divider resistance 2|2, means (such as are well known in adding machine keyboard construction) are preferably provided to prevent the simultaneous depression of more than one of the preset keys associated with a given manual or pedal clavier. However, even if two or more preset keys were simultaneously depressed, and by such action the entire voltage divider resistance 2|2 was short circuited, no serious injury to the battery 2H would result, due to the provision of fthe protective resistance ZIB.

The preselected tone qualities produced upon depressionI of one of the preset keys PK-I to PK-IO may, of course, be changed by the user of the instrument merely by changing the` connections of the conductors 200 with the conductors 202-2|0, so that any particular tone quality found especially pleasing to the musician may be rendered instantly available, merely by the depression of the particular preset key upon may be identical with that which this preferred tone quality has been set The output signals of the control tubes may be transmitted to either one or a plurality of adjustable resonant output circuits such' as are disclosed in greater detail in my aforesaid Patent No. 2,126,464. The over-all output may,` of course, be controlled by the usual swell pedal and by a, suitable tremulant device.

Modified expression control apparatus In the foregoing description, it has been. indicated that the preset keys for both manuals and the pedal clavier may have their 'switchfilngers connectable to the same set of conductors 202-2I0. With this type of circuit only the overall volume of notes played on both manuals and the pedal clavier may be controlled by means of the volume control 240. Similarly, the tremulant b such divided expression may be obtained.

In this gure a common source of direct current potential 250 may be employed to supply three tapped voltage divider resistances 252, 254, 256 for the upper manual, lower manual and pedal clavier respectively. Each of these voltage divider resistances may be similar to the voltage characters have therefore been applied to thel corresponding parts except that the sliding contact of the adjustable resistance 258 for the lower manual has the reference character 26| applied thereto. It will be noted also that the variable resistance 258 for the two manuals do not have their corresponding ends connected in the circuit. This is to illustrate the fact that divider 2I2 previously described. The voltage divider 252 for the upper manual has the potential impressed across its terminal controlled by means of a variable resistor 258 having a. ,sliding contact 260. The contact 260 may be operated by the usual expression pedal for the upper manual in a well known manner.

'I'he resistance 258 is connected to one terminal of the voltage divider resistance 252 through an adjustable resistance 262 which is shunted by a. circuit including a switch 264 which is operated by means of a cam 266 which is continuously rotated at a tremulant frequency. A condenser 268 is connected in parallel with the voltage divider resistance 25,2 so as to prevent the introduction of high frequency transients upon the periodic opening land closing of the switch 264.

The degree of effectiveness of the tremulant device is of course controlled by adjustment of the variable resistance 262. The taps of the voltage divider resistance 252 are connected to conductors' 212-280 inclusive which form .the diierent potential sources to which the switch fingers of the preset keys PK may be selectively connected in a manner as previously described with respect to Figure lb. Similarly, the draw bars 218 and their associated preset key may be provided Ato selectively connect the `conductors 212-280 to the bus bars290298 inclusive. Of course there may be two or more sets vof draw bars, each controlled by a separate' preset key, but operating in the same wayselectively toady just the potentials on the bus bars 296-288.

for the lower manual for the upper manual and is thus illustrated, and the same reference The expression device adapted to be4 although ordinarily each of the sliding contacts 260 and 26| will be connected for independent operation by an associated expression pedal, they may, if desired, be connected to a common actuating means, in which event they are preferably connected so that increasing the potential across the voltage divider 252 for the upper manual will cause a corresponding decrease in the potential across the voltage divider 254 for the lower manualand vice versa. In this way, a common pedal might be used as a simple means for determining the relative intensities of the notes upon the two manuals. It will of course be understood that if more than two manuals are provided, an additional voltage divider and associated set of circuits will be provided for each additional manual and in that event, a separate expression pedal will ordinarily be provided for eachl of the manuals. x

It'will ordinarilyl be undesirable to provide a tremulant device for the notes played on the pedal clavier, and the voltage divider yresistance 256 for the pedal clavier is therefore illustrated as having its potential controlled only by the variable resistance 258. The sliding contact 263 is connected to the sliding contacts 260 and 26| through-a common conductor which is connected to the negative terminal of the source of'direct current potential through a protective resistance 261. The adjustable slider 263 may, if desired, be controlled by meansof a separate expression pedal, or may be manually controlled. The cams 266 for the tremulant switches 264 may be driven by a small motor through suitable speed reducing gearing, the motor, or the gearing, preferably having a speed control so that the tremulant rate may be adjusted.

With the controls shown in Figure 2, the musician may conveniently balance the intensity of the tones of one manual against those of the other manual or pedal clavier so as to obtain a great variety of expression. When the circuit of Figure 2 is utilized in conjunction with that shown in Figures 1a and 1b, the tremulant device indicated as associated with the volume control 240 may be rendered inoperative whenever the tremulant devices 262, 264, 266 and 268 are in use. Due to the relative values of the resistors |89 and R1 and the condenser C1, the individual notes produced will have a gradual attack characteristic. Since there will be a charge upon the condenser C1 after the key is released, the note will continue sounding as the condenser C1 discharges through the resistance R1, and thus the decayof the note will be at a logarithmic rate. Of course the condenser C1 could be variable, or there may be provided additional condensers which` could optionally be connected in shunt with the condensers C1, thereby decreasing..the rates of attack and decay of the notes.

It will be apparent to thoseskilled inthe art y that very many changes of a similar character sources of direct current, and that the instrument will be provided with a suitable power supply system which may be a common source for supplying energy to all of the circuits, or that several of such systems or sources of current may be utilized.

It will be further understood that the values of the electrical elements utilized in the instrument given herein are intended to be illustrative only, and that there may be considerable variation in these values without appreciably affecting the results obtained, particularly if corn-v pensatory changes are made in the values of other elements. I therefore intend by the following claims to include within the scope of my invention all such similar constructions and circuits whereby substantially the results of my invention, of which merely an illustrative embodiment is disclosed herein, may be obtained in substantially the same way.

I claim:

1. In an electrical musical instrument having a plurality of terminals, the direct current potentials of which determine the intensity at which the notes of the musical scale are sounded, keying circuits for determining the direct current potentials of said terminals comprising, a plurality of sources of direct current potential of graduated voltage, a plurality of keys, a plurality of switches operated by each of said keys, each of said switches having a pair of contacts, a high resistance connection from one contact of each. of said switches to one of said terminals, there being a plurality of said high resistance connections between the contacts of a plurality of said switches respectively and a single one of said terminals, and selectively operable means to determine the direct current potentials of the other contacts of said switches. by selective connection to said sources.

2. The combination set forth in claim 1, in which said high resistance connection includes a resistor physically adjacent the switch contact to which it is connected= 3. In an electrical musical instrument having a plurality of terminals, the direct current potentials of which determine the intensities at which notes of the fundamental frequency of the musical scale are sounded, keying circuits for determining the direct current potentials of said terminals, comprising a plurality of keys, a plurality of switches operated by said keys, each of said switches having a pair of contacts, a high resistance connection from one contact of each of said switches to one of said terminals, there being a plurality of said high resistance connections between the contacts of a plurality of said switches respectively and a single one of said terminals and a plurality of selectively operable keys effective upon actuation to determine the direct current potentials of the other contacts of said switches.

4. In an electrical musical instrument in which the sound is originated electrically by a plurality of generators, each generating a signal having a fundamental frequency corresponding to that of a note of the musical scale, and'in which the intensity of the signal transmitted from each of said generators to the output ofthe instrument is i determined by the direct current potential of a terminal associated particularly with such generator, the combination of a plurality of sources of direct current potential of different values, a plurality of bus bars, means for selectively connecting said bus bars to said sources, a plurality oi keys, a plurality of switch lingers operated by each of said keys, said switch fingers being operable to contact with said bus bars respectively upon operation of the keys, and a high value resistor connected between each of said switch fingers and one of said terminals, each of said resistors being individual to its associated switch finger.

l 5. In an electrical musical instrument in which the sound is originated electrically by a plurality of generators, each generating a signal having a fundamental frequency corresponding to that of a note of the musical scale, and in which the intensity of the signal from each of said generators which is transmitted to the output of the instrument is determined by the direct current potential of a terminal associated particularly with each of said generators, the combination of a source of direct current potential, a voltage divider connected to said source and having a plurality of taps of different potential', a plurality of bus bars, means for selectively connecting said bus bars to said voltage divider taps, a. plurality of keys, a plurality of switch fingers operated by each of said keys, saidswitch fingers being operable to contact with said bus barsrespectively upon operation of the keys, and a resistor individual to each of said switch fingers and connected between its associated switch finger and one of said terminals.

6. In an electrical musical instrument in which signals having fundamental frequencies corresponding to the notes of the musical scale are electrically generated and translated into sound, each under the control of a device having a terminal, the direct current potential of which determines the intensity of the signal transmitted to the translating means, the combination of a plurality of sources of graduated direct current potential, a plurality of keys, a plurality of switches operated by each of said keys, and a plurality of high impedance circuits individual to said switches, effective upon depression of said keys to connect said sources respectively with said terminals.

7. In an electrical musical instrument in which signals having fundamental frequencies corresponding to the notes of the musical scale are electrically genera-ted and translated into sound, each under the control of a device having a terminal, the direct current potential of which determines the intensity of the signal transmitted to the translating means, the combination of a plurality of sources of graduated direct current potential, a plurality of keys, a plurality of bus bars, a plurality of switches operated by each of said keys, separate high impedance circuits to connect said bus bars respectively with said terminals respectively upon closure of said switches, and a plurality of manually adjustable contactors each connected to one of said sources and operable to connect its associated source to a selected bus bar.

8. In an electrical musical instrument having clectroacoustic translating means, the combination of a generator of a signal having a fundamental frequency of a note of the musical scale, an electron discharge device for controlling the transmission of said signal to said translating means, the effectiveness of said electron discharge device in transmitting said signal being determined by the current flow through a resistor, and a plurality of key circuits for controlling the current flow through said resistor, each of said key circuits including a key operated switch, a high resistancel element connected between said switch and said resistor, and a plurality of direct current potential sources oi' .graduated value arranged to be connected in series with said resistance elements respectively ,Y by said key operated switches, thereby to de` termine the current ow through'said resistor. 9. In an electrical musical instrument .having a plurality of generators of electrical signals having fundamental frequencies corresponding to l0 the notes of the musical scale, electroacoustic translating means, and a device for controlling the transmission of signals from said generators to said translating means, the intensity of the note sounded by said translating means being 15 determined by the direct current potential of a terminal forming part of each of said devices, the combination of a plurality of sources of direct current of graduated potential, a plurality of selectively closable circuits between each of said 20 terminals and said sources, each of said circuits including an impedance individual to it and of value which is high with respect to the impedance of that portion of said device which receives current from said terminal. 25

10. In an electrical musicalinstrument having l a plurality of manuals in which the intensity of which an expression pedal is provided for the operation of each `oi said devices.

12. The combination set forth in claim 10 in which a single expression pedal is provided for the operation of both of said devices.

13. The combination set forth in claim 10 in which a single'expression pedal is provided forl said devices and is operable to progressively increase the potential across the termina-1s of one of said voltage dividers while progressively dccreasing the potential across the other of .said

.voltage dividers.

14. The combination set forth in claim 10 in which a protective resistance is connected in series with each of said voltage dividers.

LAURENS HAMMOND. 

